This is the way to hold the bachi.
So, the shaft of the bachi goes in between the ring finger and the pinky. It may feel like a big stretch at first, but don’t give up, ’cause the next day (or the day after) it’ll feel more comfortable as your hand gets used to it.
Anywho, so the shaft is in between the ring and pinky finger. then, you take the rest of your fingers and rest them on the shaft of the bachi. Some people like to spread their fingers out. Why? For more stability? For a more ferocious look? Who knows. Afterwards, just place the thumb at the edge of the tip.
Then, place your arm on the dou and bend your wrist so the bachi is almost parallel with the skin (roughly 90 degrees). That’ll feel awkward, but just do it. It’s good wrist flexibility practice!
Two warnings: 1, even though holding the bachi in that weird position feels slightly awkwardly stiff at first, be sure to be as relaxed as you can. Your hand should be so loose that the bachi would almost slip out without the ounce of pressure you are gripping it with. (the only part of your hand that really grips the bachi is the ring and pinky finger. The rest of the fingers is just for stability.
2, Remember to do some wrist stretches before/after you play shamisen. Like physical sports, If you don’t stretch, you can not only hurt yourself, but also stiffen up.